Drilling-induced and logging-related features illustrated from IODP-ICDP Expedition 364 downhole logs and borehole imaging tools
2018
Abstract. Expedition 364 was a joint IODP and ICDP mission-specific platform (MSP)
expedition to explore the Chicxulub impact crater buried below the surface of
the Yucatan continental shelf seafloor. In April and May 2016, this
expedition drilled a single borehole at Site M0077 into the crater's peak
ring. Excellent quality cores were recovered from ∼505 to ∼1335 m
below seafloor (m b.s.f.), and high-resolution open hole logs were acquired
between the surface and total drill depth. Downhole logs are used to image
the borehole wall, measure the physical properties of rocks that surround the
borehole, and assess borehole quality during drilling and coring
operations. When making geological interpretations of downhole logs, it is
essential to be able to distinguish between features that are geological and
those that are operation-related. During Expedition 364 some drilling-induced
and logging-related features were observed and include the following: effects caused by the
presence of casing and metal debris in the hole, logging-tool eccentering,
drilling-induced corkscrew shape of the hole, possible re-magnetization of
low-coercivity grains within sedimentary rocks, markings on the borehole
wall, and drilling-induced changes in the borehole diameter and
trajectory.
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